This invention relates to the soldering of radio frequency shields to printed circuit boards.
It is often desirable to partition a printed circuit board into separate areas by means of RF shielding members so that RF energy may be contained within, or excluded from, the partioned areas to eliminate the undesirable effects caused by interference due to stray RF signals. Such shielding is used extensively in RF tuners of television receivers. The term "printed circuit board" as used herein refers to circuit boards having electrical conductors formed on one side by deposition, etching or any other process.
Modern television circuit board assemblies are generally manufactured by mounting components on the component side of a printed circuit board with their leads extending through the boards to conductor pads on the conductor side of the board and then wave soldering the leads to the conductor pads on the conductor side of the board and then wave soldering the leads to the conductor pads. Thus all electrical connections between the mounted components and the printed circuit board conductors are accomplished quickly and economically. In addition, wave soldering tends to produce more reliable electrical connections.
RF shields are typically mounted on the component side of the circuit board by passing the tabs of the shield through slots formed in the board. While it is desirable to wave solder the shields to the ground conductor of the board, it has been found that the tabs are obstacles in the path of the solder wave and in some instances produce undesirable splash effects and also tend to block the solder wave from reaching conductor pads immediately behind the tab. Therefore, shield members have typically been hand soldered to the printed circuit board after the wave soldering process. Since the tabs are not present until after the wave soldering operation, they do not interefere with the wave soldering process. This method requires a hand soldering operation for each shield member mounted on the circuit board, a costly and time consuming process.
Another solution to the problem of soldering shield members to printed circuit boards is to form the tabs of the shield such that when the shield is mounted on the printed circuit board the tabs are substantially flush with the surface contacted by the solder wave. This solution has several inherent problems. Since the tabs may no longer provide the friction necessary to hold the shield in place during the soldering process, smaller "holding tabs" are sometimes provided. These holding tabs are inserted through slots in the circuit board and twisted to retain the shield in place. This requires an extra "twisting" step in the mounting process. Perhaps more importantly, the larger tabs form an RF shield on the conductor side of the board. By cutting these tabs flush with the surface of the board the benefits of shielding the critical circuit from the conductor side as well as the component side are lost.
Therefore, it is desirable to provide an apparatus which allows wave soldering of shield members with relatively large tabs intended to extend below the printed circuit board to which the shields are mounted which reduces solder splash effects and the blockage of the solder wave by the tabs.